How Can I Deform a Cloth During Simulation?
Use a hook modifier with pinned vertices.

First, add the vertices you want to use to move the clot up to the same group as your other pinned verts (the ones that hold the cloth at the waist).

Now you need to add a hook object like an Empty in the region you want the cloth to move. 

To your cloth add a hook modifier. Select the hook empty and the pinned vertex group. Set the radius to something small so it doesnt interfere with the sim until you need it to.
Make sure the hook is above the cloth modifier in the stack.

Let the sim run.

Once it gets to the point where you need to manipulate the cloth, move the empty and the vertex group will be "pulled" alongside the empty.